Exposure of guinea pigs to cotton dust results in an acute respiratory response characterized by "rapid shallow" breathing and airflow disturbance. The same response has been obtained upon exposure of animals to aerosols of acetone-extracted Enterobacter agglomerans and to lipopolysaccharides from E. agglomerans. The current study compared the potency of endotoxins derived from three microorganisms: E. agglomerans, Ps. syringae and E. coli to cause respiratory responses in guinea pigs. Animals were exposed for 6 hr to aerosols of the purified endotoxins. Endotoxin from the two bacteria found in cotton dusts, E. agglomerans and Ps. syringae had identical potency. The response to E. coli endotoxin was measurably less. These results indicate that endotoxins from a variety of Gram-negative bacteria can cause acute respiratory responses in guinea pigs and that the two most prevalent Gram-negative bacteria in cotton dust have identical ability to produce this response.